[FIX] website_slides: article content plain text visible in fullscreen

Steps to reproduce:

- Get the eLearning App.
- Go to an existing course or create a new one.
- Add a new content of type article.
- Go to website preview and to edit this slide.
- Write plain text inside the box of content.
- Go to Fullscreen.

The issue is that we are using `.append()` and this expects that we pass
it an html or a jquery object which is not the case when we just type
plain text inside it, so using `.html()` will allow us to render any
content as HTML.

opw-3265113

closes odoo/odoo#144818

X-original-commit: 34b78a6619888ebbc6e67b5c474260453a7ed84b
Signed-off-by: Thibault Delavallee (tde) <tde@openerp.com>

addons/website_slides/static/src/js/slides_course_fullscreen_player.js

@@ -668,7 +668,7 @@
                 $content.empty().append(renderToElement('website.slides.fullscreen.video.google_drive', {widget: this}));
             } else if (slide.category === 'article'){
                 var $wpContainer = $('<div>').addClass('o_wslide_fs_article_content bg-white block w-100 overflow-auto');
-                $(slide.htmlContent).appendTo($wpContainer);
+                $wpContainer.html(slide.htmlContent);
                 $content.append($wpContainer);
                 this.trigger_up('widgets_start_request', {
                     $target: $content,